Total Organic Carbon and Formation Evaluation with Wireline Logs in the Green River Oil Shale

Abstract

AbstractA well drilled in the Green River formation in Colorado on the Bureau of Land Management RD&D lease of American Shale Oil LLC (AMSO), provides an opportunity to compare core measurements and log-derived properties in a unique unconventional resource reservoir. The core was analyzed for matrix density, Fischer Assay, total organic carbon (TOC), mineralogy, and 58 inorganic elemental concentrations. Logs include neutron, density, gamma ray, resistivity, magnetic resonance, and inelastic and capture nuclear spectroscopy. The data from this well are used to demonstrate new methodologies to estimate the TOC content and Fischer Assay oil yield.The TOC content is estimated in three ways. The first is a multitool petrophysical evaluation. The second is an estimation of kerogen from the difference between density and magnetic resonance (MR) porosities where MR porosity corresponds to the water-filled porosity and density porosity to the sum of kerogen-and water-filled porosity. The third method combines inelastic and capture nuclear spectroscopy log data to compute elemental concentration logs of total carbon, inorganic carbon, and TOC.For comparison of core mineralogy and chemistry with log data, over 200 intervals of core from this well were sampled as 2-ft-long slabs that were ground and homogenized, approximating the vertical resolution of log responses. The agreement between the logs and core values for total carbon, total inorganic carbon, and TOC is very good. The TOC log is used to activate empirical relationships such as Fischer Assay oil shale grade from TOC, again with good results.